The present invention relates to an apparatus for preheating the material to be charged into steel making equipment.
In steel making processes, it is desirable to preheat materials, such as scrap, alloy iron, directly reduced iron and lime, before they are charged, for example, into electric furnaces.
The steel making material is preheated to avoid a steam explosion accident when it is charged into the furnace for safety operation and to achieve an improved steel making efficiency by promoting melting of the material.
While auxiliary burners are most widely used for preheating the charge, such devices are not favorable for savings in energy. Accordingly apparatus have been introduced into use for recovering heat from the hot exhaust gas released from electric furnaces, at a location between the furnace and a dust collector for forcedly discharging the gas from the furnace. However, these apparatus have the following drawbacks.
Basically the apparatus is as low as, for example, 20 to 30% in heat recovery efficiency and is unable to fully preheat the charge, necessitating a long period of time for steel making operation. Conversely if it is attempted to improve the recovery efficiency, the preheating apparatus must be made large-sized and complex at an increased cost. Thus the apparatus fails to achieve savings in energy as desired. Additionally, the preheating apparatus, if large-sized, requires a prolonged cycle time for supplying the charge to the apparatus and withdrawing the charge therefrom. This will reverse the current trend of steel making techniques toward a shorter melting time, hence objectionable.
Furthermore the conventional preheating apparatus, which must fulfill the requirement of shortening the cycle time, is nevertheless cumbersome to operate, while the apparatus still remains to be improved in ensuring safety of operation.
The conventional preheating apparatus has another problem. Because of the low heat recovery efficiency, the gas released from the apparatus to the atmosphere has a relatively high temperature (e.g. 150.degree. C.) and therefore contains a large amount of oil mist, etc. When released to the atmosphere along with the exhaust gas, such mist produces a white smoke to cause air pollution.